Prevention of amine losses in gas treating systems



Aug. 26, 195 H. D. FRAZIER 2,608,461

PREVENTION OF 'AMINE LOSSES IN GAS TREATING SYSTEMS Filed March 26, 1949 So/uzr'on r -n 12 I- 21 Gas In i I Ric/1 .So/uzfon 11 N Conzaczor (onfbczor .AENQY 12 1 1242152,

IN V EN TOR.

Patented Aug. 26, 1952 PREVENTION or AMmE LossEs IN GAS TREATING sYs'rEMs Henry I Fra zier", Alhambra, Calif., assignor to q The Fluor, Corporation; Ltd., Los Angeles, Calif., a corporation of California i This; invention'has to do generally with improvementsin gas treating processes employing liquid 'amine solutions reactive with acidic cons'tituents of the gas to free the latter principally from cori'osive'impur'ities, and is directed particularly to new methods for theprevention of amine losses from the treating system, arid-undesirable amine accumulations inthe gas transmission lines. i j

In the usual gas treating'systems employing "amine-containing solutions for the purpose of removing: he acidic constituents from gas streams, and also in somesystems for dehydration io'f 'the g'a's stream, the last contactofthe gas with the leans'olution serves to equilibrate the gas stream with the mmem the solution. This equilibration results in the introduction into the as stream of a def nite amount of the amine along withsonieof each. of the other constitu ents of thes'olution'. This amountqf the amine ordinarily is lost to the plant operations. Low "er ed temperatures in the pipe line leading from the plant may cause some amount of the material to be condensed in the pipe. This condensation results inadrop of the efiiciency of the "pipe line. especially since it is mixed with foreign matter from thepipe and is spread along a great lengthof the line. The amount not condensed is lost entirely and is nonrecoverable by present methods; j In accordance withthe invention, the amine ordinarily lost is recoverable for return and reuse in the plant; all by a simple and'eifective procedure; In presently operating commercial plants vusing.for--example-a solution of approximately 20% monoethanolamine. 5% water and 75% diethylene. glycol, the solution is so efiicientdn treating the as for-.the removal of acid asconstituents. that unless the plant is overloaded there may b'ejno appreciable .carbondioxide or hydrogen sulfide in the 'fefliuent as. Overloading the plant to the point that it will pass carbon dioxide, 'will also cause thepassage of an undesirable amount=of h rogen suliide. I have discovered that ifan acidic compound be injected into the gas stream after its last contact withthe lean amine treatin solution. the acidic com ound will combine with'thelamine entrained (either as liquid or vapor) in the with resultant formation of a compound having a molecular weight much higher thanthe amine, and having also a correspondin ly lower vapor pressure. To illustrate, and-assumin carbon dioxide to be added to the gas stream treated with a solution containing monoethanolamine having a molecular weight sum. This heavier compound then is precipitated 61) and may be removed fromthe "gas by any ofthe 4 Claims.

and i japmias'tioii March 26, 1949, Serial No. cares (class-#2) methods: later-described. Ordinarily the acidic compound'will be injected in amounts between hom /t and 5 of the gas stream to'which itis added. i i a It will be understood that, the invention contemplates the use and recovery of anyof the normally liquid amines reactive with acidic cone stituents of thegas being treated. Typically, the usable amines are included in the aliphatic amines, in which the amino radical is attached to a carbon atom, which in turn may be attached to one or more aliphatic or straight chain groups, saturated or unsaturated, or to a saturated or unsaturated ringstructure. These amines include the primary, secondary and tertiary forms as Well as members of the mono, di-, and triamine series.

Further and broadlycontemplated is the use of "any suitable acidic compound, preferably a gas, for reaction with amine entrainment carried by the gas stream. Illustrative acidic compounds are sulfur dioxide, hydrogen chloride, carbon disulfide, acetic acid and formic acid. Because however of such considerations as greater facility in use, fewer corrosion difliculties and the capaci vty of the reaction product for simple regeneradioxide as the Fig. 24s a view similar to Fig. 1 illustrating a variational embodiment of the invention. Any-gaseous mixture containing an acidic constituent, typically hydrocarbon natural gas or refinery gases containing either or both carbon dioxide and hydrogen sulfide, is fed to the con tactor column 10 through. the inlet line I l. The gas flows upwardly through the chimney drawoif my and then through liquid and gas con tacting means such as the diagrammaticallyin- .d'icated bubblecap trays [3 to the top .of -the column, in intimate mixture with the down-flow:-

ins lean amine solutionjintroduced to the column through linemMr V Therich solution, containing absorbed a'cidic constituents of the gas is removed :from the base-of the column through line IE to be regenerated in the usual still (not shown) and returned=to the contactor through line M. The

lean ab-sorbentsolution may consist of: an aqueous amine solution containing say from 10-15% aliphatic amine (e. g. monoethanolamine) in umn through line I6 may contain appreciable quantities of entrained aminercarriodover, from. the top tray of the column, and which, is, desirr. ably recoverable from standpoints both of preventing undesirable accumulationsin the: gas:

line, and of avoiding the loss-of-valuableamine. In accordance with the invention I introduce to the gas stream that has left thecirculated amine? solution in the column, an acidic compound, preferably an acid gas, reactive with the entrained" amine to convert the latter to a relatively high molecular weight,- low vaporpressure-compound readily recoverable and separable from the treat-w ed gas: The preferred acidic-additiveis carbon dioxide which may be introduced through line" to-the gas stream flowing through pipe- IS, the proportion of carbon dioxidethus introduced being'suflicient to effectively convert theentrained amineto'the relatively low vapor pressurexcarbamate. The resulting mixture maybe passed into'aseparator l a from which the treated'gas leaves-through line l'9, and fromthebase of'which liquid entrainment including the carbamate; is withdrawn through line 26. It will be under- 'stoodthat the separator I 8may be placed in the treated gas line- IG-at any location however re.- mote-from the contactor Iii. If desired, the car-'- bamate may be recovered and subjected toregeneration along with the amine solutioncirculated through the contactor. Accordingly, the liquid recovered in line 20 may be returned to the gastreating cycle at any appropriate location, as through'line 2| to the base of the contactor and into the rich solution going to the-still.

:In some instances it may be desirable to recover fromthe treated gas leaving the contactor, liquid entrainment er -condensate including thecarbamate-at some location in the gas distribution system following its compression. Accordingly, inFig 2,- the gas stream beyond the separator l'8-shown to be passed through line 22 into conventionally illustrated compressors-23 into a second separator 24 from the base of which the removed liquid, including the carbamate, is directed through line 25 for further disposalorreturn to they c'on'tactor by wayof'lines 20 and '2 I.

flowing-from the contactor, itis' contemplated that it desired, such admixture of the gas with the acidic additive maybe efiected' in the contactoritself at a location above the departure bith'e gasstream from the circulated amine-absorbent; Thus as shown inF-ig. 2 the lean solutions may be introduced to the contactor- 21 through line ata location below't-he top of the colui'i in-adistance sufiicient to acc-ommod'ate a numbei ofbaflles or trays 29 below which the carbon dioxide is introduced through line 30. Here thefunction of the top trays 29is primarily to effect intimate admixing of the main gas 'stream with-theadded carbon dioxide to a degree s-ufiicien-t. for conversion of substantially all the amineentra-inedin the gas from the entering-lean solution, to-thecarbamate; As it accumulates on the top trays 2,9, the carbamate drains-down in thecolumn to join the--, down fiowingyleair solur ti-oni and; ultimately be omes, re enerated; in the 7 still;

Other processes having for their object the minimizing oi arnine lossesjromthercontactor in this type oi gas' treating -prccess: are-disclosed in a copending Frazier and Kohl application Ser;

; No. 83,739, filed March 26, 1949, on Systems for theTreatInenLoi Gases, and the Frazier and Biesenifeld application, Ser. No. 83,740, filed March 26, 1949, on Amine Absorbent Gas Treating Systems I claim;

1. The-method that includes passing down wardly througha; contacting zone a solution of a liquid amine in contact with a gas stream flowing-upwardly through the zone and containing carbon dioxide reactive; with the amine, and inro uoine carbon d ox cztc th sasstream' af r a d: he ting; he reacti n: produota mrecoy rz ie amine.

2. The, method or;-prevent n mmar o siim gas stream passed;-upward1v-th1t9ugll and .-oiu 1 a contactor column in contact with a downrflqw ing solution ofa liquid amine 1 reactivawith; an acidic constituent in the-gas andintroduced to an upper, location insaid column, that include-3:1 1: troducing carbon dioxide to the-gasstreamaiter its passage through said: columnto convert the amine to av relatively high molecular weight, and low vapor-pressurereactionproduct.

3. The method of; preventing amine;:.loss-:in;a gas stream passed upwardly through, and out of acontactor column in. contact; with a down: fl wing o ut on, of a. l quid amine-r active w th carbon dioxide contained, in thegas; and intro,- duced to an; upperlocation ,iirthe o umnibelow a top, section. thereof, that .inc1udes-in.t f0.ducing carbon dioxide to the gas, stream insaidtop sec tionof thecolumn to-, convert amincsentrained in he. as to. a recovera le .r a v lahish. mole ular weight andlow. vapor; pressure; reaction product, and returnin idprod ct: t he aminesolur 4. The method that includes continuously cir culatinga solutionof, a: liquid amine throu'g-h a hea and reg nerat n zoneandthmimm n inlet downwardlythrough a contacting zone passing gas" containing an; acidic constituent -of-= the group consisting I of hydrogen sulfide and carbon dioxide and reactive with theamineupwardly through and Out'of-sald' zone'in contact with the in o t intr du ing arboni ioxideato the; gas treated by c ntactawithitho.. lu ionand ate locat on beyondsaid. nlet to onvert amine ntrain din heses toa relatively-hiehzmoleoular w i t, and low vapor, pres re r action product a t, and return n m dst-c tion; roduct-to; he circulated; am ne lutiqnzfflr i ating and recovers-citric.-amineqinth heating-zone;

HENRY-DrE-EAZI'ER;

EEFERENGES; circa The following references: record. my the file of' this patent: Y Y

UNITED s'riir s Ear in s i "Date? 

4. THE METHOD THAT INCLUDES CONTINUOUSLY CIRCULATING A SOLUTION OF A LIQUID AMINE THROUGH A HEATING AND REGENERATING ZONE AND THEN FROM AN INLET DOWNWARDLY THROUGH A CONTACTING ZONE, PASSING GAS CONTAINING AN ACIDIC CONSTITUENT OF THE GROUP CONSISTING OF HYDROGEN SULFIDE AND CARBON DIOXIDE AND REACTIVE WITH THE AMINE UPWARDLY THROUGH AND OUT OF SAID ZONE IN CONTACT WITH THE AMINE SOLUTION, INTRODUCING CARBON DIOXDE TO THE GAS TREATED BY CONTACT WITH THE SOLUTION AND AT A LOCATION BEYOND SAID INLET TO CONVERT AMINE ENTRAINED IN THE GAS TO A RELATIVELY HIGH MOLECULAR WEIGHT AND LOW VAPOR PRESSURE REACTION PRODUCT 